Composite containers where the outer surface of the liner is reinforced with an FRP layer are used in various fields. In fuel cell cars for example, a composite container, where an FRP layer is formed on the outer surface of a light metal liner made of an aluminum alloy coated with an insulating paint, is used as a high pressure tank in a long, cylindrical form that is to be filled with hydrogen gas and mounted in a car.
A filament winding method is used to wind FRP around a metal liner or the like in order to form a composite container. Patent Document 1, which is described below, discloses a composite container where carbon fibers or glass fibers that are impregnated with a thermosetting resin such as an epoxy resin are used as FRP, and hoop winding FRP layers (which are referred to as hoop layers) and helical winding FRP layers (which are referred to as helical layers) are wound around a metal liner for reinforcement along the liner axis in the longitudinal direction of the metal liner in accordance with a filament winding method.
Here, hoop winding refers to a winding method according to which FRP are wound around the cylindrical section of the liner in the direction of the circumference, and concretely refers to a winding method according to which FRP are wound around the cylindrical section at a winding angle of 86 to 90 degrees relative to the direction of the axis of the liner (hereinafter, referred to as an orientation angle). The hoop winding allows adjacent FRP to make contact with each other without a gap between the FRP when being wound. Meanwhile, helical winding refers to a winding method according to which FRP are wound in a helical form passing from one of the dome sections (also referred to as mirror sections) of the liner through the cylindrical section to the other dome section at an orientation angle that is constant at an angle of 85 degrees or less. In the helical winding, a gap is created between adjacent FRP.
FIG. 8 is a diagram illustrating an example of the cross-section structure of a conventional composite container. In a long composite container as one for being mounted in a car, at least one hoop layer 2 and at least one helical layer 3 are layered on top of each other on the outer surface of the liner 1 in order to reinforce the strength of the pressure container. In the example in FIG. 8, three hoop layers 2 and three helical layers 3 are alternately layered on top of each other in order to increase the strength of the reinforcement.
Between these layers, hoop layers 2 are wound solely for the purpose of reinforcing the strength of the cylindrical section 4, whereas the helical layers 3 are wound for the main purposes of reinforcing the area around the left and right dome sections 5 and 6 and reinforcing the strength of the liner 1 in the direction of the axis.